High-pressure discharge lamps, and particularly such lamps having a metal halide fill are used more and more for general service illumination. Another use of these lamps is for headlights in automotive vehicles. The power requirements for lamps of either application is usually below 70 W. 35 W is entirely sufficient for headlight illumination. Automotive lamps must be so designed that maximum available light is obtained practically instantaneously after closing of the power supply switch. High-pressure discharge lamps, while being extremely efficient for illumination, have the disadvantage that some starting time is required until the lamp, after first ignition, provides a high output light flux. In conventionally operated lamps, such starting time may be in the order of about 40 seconds.
German Utility Model Publication DE-GM 86 23 908 proposes a solution to shorten the starting time. External heat is supplied in order to vaporize the fill within the lamp, and retain it under vaporized condition. The increased temperature, and hence the increased pressure, permitted shortening time, that is, the time after closing of the main power supply switch, to only about 8 seconds. This, still, is too long for automotive headlight use, and the external heating of the lamp requires additional electrical energy. This increases the installation, the terminal constructions, and does not entirely solve the problem of fast light output response of the lamp. For many uses, the delay between switch operation and high light output is still too long.